US2764242A

US2764242A - Prevention of casing corrosion

Info

Publication number: US2764242A
Application number: US351831A
Authority: US
Inventors: Gilson H Rohrback; Joseph F Chittum
Original assignee: Individual
Current assignee: Individual
Priority date: 1953-04-29
Filing date: 1953-04-29
Publication date: 1956-09-25
Anticipated expiration: 1973-09-25

Description

vSept. 25, 1956 G.. H. ROHRBACK ETAL 2,764,242

' PREVENTION OF CASING CORROSION Filed April 29. 1953 2 Sheds-Sheet 1 l S RFACE CA ING AIR CEMENT DRILLI G M D COR OSIOI :HIGH PRESSURE SALT WATER PRODUCTION TUBING L CASING Flew INVENTORS G/LSON' H ROHRBACK JOSEPH F CH/TTUM BY M ATTOR YS P 1956 G. H. ROHRBACK ET AL 2,764,242

PREVENTION OF CASING CORROSION Filed April 2-9, 1955 2 Sheets-Sheet 2 B B 4 \\\\U I 2 l I 6 I! A A FIG.2

INVENTORS G/LSON H. ROHRBACK United States Patent PREVENTION or CASING coRRosmN Gilson Rolrrback, Seattle, Wash, and Joseph F.

Chittum, Whittier, Calif.

Application April 29, 1953, Serial No. 351,831

4 Claims. or. 166-1) This invention relates'to a composition and method for inhibiting the corrosion of oil well casings.

Although relatively little attention has been given to corrosion failure of oil well casings in the literature, this problem is rather wide-spread. A number of theories have been proposed to account for casing corrosion and some attempts to control it have been made on the basis of the theories. Among the theories heretofore advanced to explain casing corrosion have been suggestions that the corrosion was due to bacterial action; due to electric currents flowing through thecasing; due to localized corrosion at metal flaws; due to particular compositions of formation water; due to corrosion by selfpotential currents, and due to interzonal migration of salt water. So far as is known, no successful method of controlling casing corrosion has been developed on the basis of any of these theories. Meantime, casing failure due to corrosion continues to be a serious problem in many oil fields. Repair of casing failure is difficult at best and if the failure escapes detection for an appreciable period of time, the well ceases to produce and production may not be resumed, even though the casing be repaired, necessitating abandonment of the well.

Thirty instances of casing failure due to corrosion in I a California field were carefully studied. The average time of failure was about five years, but failures occurred at times ranging from less than one year to about sixteen years from completion of the well. In the large majority of these cases the failure occurred in the salt water zone above the cemented zone. Corrosion of the casing in all instances was highly localized and from an overall study of the circumstances attending these casing failures it was concluded that the-corrosion was electrochemical in character and occurred when a part of the casing was in contact with low (7-8) pI-l formation waterand a part of the casing was in contact with higher "(8 to 12) pH mud or with higher (8-12) pH washing solutions. The situation existing in the well when serious .corrosionis encountered will be better understood by reference to Fig. l of the appended drawings, which is a diagrammatic illustrationof a section of a typical well casing and formation. The portion of the casing in contact with formation water ofrelatively low pH is the area at which rapid corrosive attack appears to occur.

It has now been found that casing corrosion can be very markedly inhibited by filling the annular space above the cemented zone and between the casing and the formation with an aqueous clay drilling mud containing .001 .to 2.5%- by weight of ferrous chloride or stannous chloride. When a well has been drilled to the desired depth and is ready for a cementing operation, the casing is full of drilling mud. Cementing of the casing is commonly accomplished by forcing a cement slurry (optionally preice of cement slurry has been introduced into the casing, the cement is forced into position between the outer casing wall and the formation by pushing it down the casing with additional mud. When the cement is in place it is allowed to set and that portion of the annulus between the outer casing wall and the formation and above the cemented zone is filled with drilling mud which was pushed ahead of the cement slurry. This drilling mud should have a substantial content of either ferrous chloride or stannous chloride in order to prevent casing corrosion. Similarly, it is desirable that the mud introduced into the casing to force the cement into position and which is ultimately resident in the annulus between the casing and the formation below the cemented zone should also be treated so as to have an appreciable content of either ferrous chloride or stannous chloride.

While ferrous chloride and stannous chloride are the preferred ferrous and stannous compounds for use pursuant to the invention, it is the ferrous and stannous ions which are the effective inhibiting additives. Accordingly, other ferrous and stannous compounds which are soluble or dispersible in aqueous fluids such as the sulfates, the nitrates, the hydroxides, can be used instead of the chlorides in equivalent amounts and are found essentially equally effective.

During the drilling of a well the mud is continually circulating and is continually in contact with the air. No advantage is obtained by adding ferrous compounds or stannous compounds to the mud used during the drilling, since the regular and intimate contact with the air in the mud pits would cause oxidation of stannous and ferrous compounds to the corresponding stannic and ferric compounds which are useless in preventing corrosion. Accordingly, the stannous compound or ferrous compound must be added to that portion of the mud which will be left between the outer casing wall and the formation when the well is completed just prior to introducing this portion of the mud into the well. Both stannous chloride and ferrous chloride, especially the latter, increase the viscosity of aqueous clay muds and increase their rate of filter loss.

It has been found that corrosion can be inhibited without adverse effect on the viscosity and water retaining properties of the mud by adding a corrosion inhibiting concentrate consisting essentially of a mixture of 4 to 20 parts by weight of stannous chloride or ferrous chloride and 2 to 10 parts by weight of a water loss reducing agent to that portion of the mud which will ultimately be resident between the casing wall and the formation immediately prior to the introduction of that mud into the well. Suitable water loss reducing agents are starch, natural gums, such as gum arabic, gum tragacanth, Indian gum, and the like, or the alkali metal salts of carboxymethylcellulose. The carboxymethylcellulose materials are especially suitable and mixtures of ferrous chloride and the carboxymethylcellulose salts containing between 1 and 10 parts by weight of ferrous chloride per part by weight of the carboxymethylcellulose compound constitute especially suitable corrosion inhibiting concentrates.

It is frequently desirable to employ a corrosion inhibiting concentrate containing a viscosity reducing agent in addition to the ferrous chloride and water loss reducing agent. For example, suitable concentrates will contain from 4 to 20 parts by weight of ferrous chloride, 2 to 10 parts by weight of a water loss reducing agent, and 3 to 30 parts by weight of a viscosity reducing agent. Mud viscosity reducing agents are well known to those skilled in the art and include the molecularly dehydrated phosphates or polyphosphates and plant tannins such as quebracho extract and chestnut extract. An especially desirable concentrate is one containing 4 to 20 parts by weight of ferrous chloride, 2 to 10 parts by weight of an alkali metal salt of carboxymethylcellulose, 3 to 12 parts by weight of a sodium polyphosphate, such as sodium meta-phosphate, sodium tetraphosphate, sodium tripoly- 4 by the fluid of lower pH. The electrodes were then left in these relative positions for a period ordinarily of 14 days, at the end of which electrode 4 was removed and weighed to determine its loss of weight. In order to dephosphate, tetrasodium pyrophosphate, sodium hexa-rneta- 5 termine the weight loss of electrode 4 due to electrophosphate, and the like, and 4 to 20 parts of quebracho. chemical action alone, a second small iron-strip approxi- The inhibitor concentrates described above are added mately i ntical with electrode 4 in Size andshape Wa to the mud amount sufficient to give the mud a ferrous suspended from the Wall 0f the i in Same fluid chloride content in the range from 0.001% to 2.5% by whiehsllffellllded electrode the end of the test weight. Compositions of typical d treated d o period the weight loss of electrode 4 and the weight loss treated are indicated below. The untreated mud had a of the Second metal p. e determined and the density of 90 pounds per cubic foot and a pH of 11 terence between these two losses was the loss of weight of electrode 4 due to electrochemical action. Results Untreated Treated of a series of experiments are set forth in Table I be- Po u ds P05123 15 low. The muds employed in the tests were typical com- 33 33 2 3 mercial drilling muds. The formation water was a typical of Mud 0f Mud aqueous effluent from a California well and the .pyrofluid was an aqueous solution of tetrasodium pyrophosphate gigg %.288 such as is commonly employed for washing the mud gg gfi 'flfigflhigg' jj" Nono cake prior to introduction of the cement and which is $222 gf lf l gg commonly left in the annulus between the outer casing quebrachounir p wall and the formation when the well is completed. The Sodium Hydmxide 150 150 efiect of various additives on the weight loss due to electrochemical corrosion is shown in the table.

TABLE I Weight loss in corrosion cells for difierent combinations of treated and untreated fluids Electrode 1 Electrode 4 1\{easurcd Vcight Test No.

Fluid Additive Loss from Electrode 4 Due to Ourrent (Milllgrems) pH Fluid Additive pH N one Quebracho Sodium Ohrornate.-.

. Formation Water- 2-Mud contained quebracho-OAZ percent.

Laboratory studies of the nature of casing corrosion and of compositions and methods for controlling it were made in the apparatus diagrammatically illustrated in Fig. 2 of the drawings.

In the drawing container 6 is a glass jar having about 4 gallons capacity. Electrode 1 Was made up of three short sections of concentric pipe welded together. The weld areas were covered with a plastic paint to eliminate undesirable galvanic couples from these areas. The total area of this electrode was about 330 square inches. Electrode 4 is a small strip of iron having a surface area of approximately 2 square inches. Electrode 1 is welded to iron rod 2 which is attached to adjustable support 5 so that the position of electrode 1 in the jar can be adjusted at will. Electrode 4 is connected to rod 2 by wire 3. In making the experimental tests to fluids were introduced into jar 6. The fluids differed from each other in both pH and density. In each test, jar 6 was positioned in the jar so that it was entirely surrounded pletely eliminated by the addition of eitherferrous chloride or stannous chloride to the high pH fluid, which in practical effect means the addition of these materials to the mud and to the pyrowash solution if such a solution is used in completing the well.

l. A corrosion inhibiting concentrate, suitable for addition to aqueous clay drilling mudto be left in the anfilled with the denser of the two fluids employed to level nular space between the casing and the formation of a AA and then the less dense of the two fluids was introcompleted oil well, consisting essentially of 4 to 20 parts -duced into jar 6, filling the jar to about level BB. Elecby weight of a material selected from the group controde 1 was positioned in the jar so that it wasentirely sisting of stannous chloride and ferrous chloride and 2 surrounded by the fluid of higher pH. Electrode 4 was r to 10 parts by weight of a water loss reducing agent.

2. A corrosion inhibiting concentrate suitable for addition to aqueous clay drilling mud to be left in the annular space between the casing and formation of a completed oil Well consisting essentially of ferrous chloride and an alkali metal salt of carboxymethylcellulose containing 1 to 10 parts by weight of ferrous chloride to each part by weight of carboxyrnethylcellulose.

3. A corrosion inhibiting concentrate, suitable for addition to aqueous clay drilling mud to be left in the annular space between the casingand the formation of a 1 completed oil well, consisting essentially of 4 to 20 parts byweight of ferrous chloride, 2 to 10 parts by weight 'of an alkali metal salt of carboxymethylcellulose, 3 to 12 parts by Weight of an alkali metal polyphosphate and 4 to 20 parts by Weight of quebraeho.

4. The method of preventing external corrosion of oil well casing which comprises filling the annular space above the cemented zone and between the casing and the formation with an aqueous clay drilling mud containing 0.001 to 2.5% by weight of a material selected from the group consisting of ferrous chloride and Stannous chloride.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Hoar et al.: Data on the Use of Stannous Chloride as a Pickling Inhibitor, article in Chemical Abstracts, vol. 35, 3936, 1941.

Claims

1. A CORROSION INHIBITING CONCENTRATE, SUITABLE FOR ADDITION TO AQUEOUS CLAY DRILLING MUD TO BE LEFT IN THE ANNULAR SPACE BETWEEN THE CASING AND THE FORMATION OF A COMPLETED OIL WELL, CONSISTING ESSENTIALLY OF 4 TO 20 PARTS BY WEIGHT OF A MATERIAL SELECTED FROM THE GROUP CONSISTING OF STANNOUS CHLORIDE AND FERROUS CHLORIDE AND 2 TO 10 PARTS BY WEIGHT OF A WATER LOSS REDUCING AGENT.